New York: Hurst and Company, (c 1910). Hardcover - The first book in this series described by the publisher as one which marks "a new era in boys' books - the wonders of modern science epoch." Features Frank and Harry Chester who, with their $10,000 prize airplane, rescue a chum from death, discover a lost treasure valley and more. Glossy frontispiece and 4 inserted plates on plain paper. The publishers claim that a million copies of this series have been sold. 336 pp plus 8 pp publisher's ads.